Read about the description and design of retaining walls and soil reinforcement procedures
The operational principles of an MSEW system are based on the interface friction between linear reinforcements and the structural filling soil, meaning its geotechnical characteristics (friction angle, cohesion, and particular weight), and are critical factors that enable the system to function.
Lengths, cross sections and the soil reinforcement required are designed according to the earth pressure of the backfill soil, of the in situ soil and according to the eventual surcharges upon the reinforcements and the back of the reinforced structure. The reinforcement required is determined based on the tensile stresses transmitted to the structural soil through the effect of the interface friction.
The design of reinforced soil walls and abutments should follow the principles involved in conventional earth retaining structures, however, reinforced soil structures require additional consideration concerning soil-reinforcement interaction.
The analysis should cover external and internal stability. External stability covers the primary integrity of the reinforced soil structure as a unit, while internal stability covers all areas relating to internal behavior mechanisms. These two analyses are essential considerations for the design of reinforced soil structures and engineers may be familiar with the tie back wedge method and the coherent gravity method of reinforced soil design.
The tie back wedge method follows basic design principles currently employed for classical or anchored retaining walls using extensible reinforcement. It has evolved from the utilization of all forms of permitted reinforcements. The coherent gravity method is based on the monitored behavior of structures using inextensible reinforcements and has developed over some years from observations on a large number of structures, corroborated by theoretical analysis. Reinforced soil stabilization structures should be designed to conform to:
- The Ultimate State
- Serviceability limit state.
In the ultimate limit state relevant potential collapse mechanisms are identified and considered together with limit state factors. In the serviceability limit state, the structure is checked to ensure that it will retain the characteristics necessary for it to fulfill its function throughout its life without the need for abnormal maintenance.
Field observations have shown that lateral earth pressures in the upper reaches of a wall will be influenced by the axial tensile stiffness of the reinforcement. For inextensible reinforcement, lateral earth pressures approximate to K0 forces and retaining structures (following the above design) should be created using the coherent gravity method.
The ultimate limit state and serviceability limit state should be checked in both approaches. The routine procedure is to design for the ultimate limit state and test the serviceability limit state. Both approaches consider the design of reinforced soil and anchored earth structures. Design should usually be based on the assumption of a two-dimensional plane strain condition.
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